Anisotropic refractive indices of organic crystals of thiophene/phenylene Co-oligomers determined by microspectroscopic measurements

We have measured and determined the anisotropic refractive indices of thiophene/phenylene co-oligomer (TPCO) crystals. The refractive indices were calculated from the crystal thicknesses and optical path lengths on the basis of the interference of the reflectance spectra measured along the crystal axes by a polarizing microscope with a white light source. The higher refractive indices were observed along the crystal short axis and this was attributed to a denser molecular packing along that axis.